1. Field of the Invention
The present invention relates to a radio device, and more particularly to a radio device in an ad hoc network that is formed autonomously and instantaneously using a plurality of radio devices.
2. Description of the Related Art
An ad hoc network is constructed autonomously and instantaneously by mutual communication between a plurality of radio devices. In an ad hoc network, if two communicating radio devices are not present in each other's communication areas, a radio device positioned between the two radio devices functions as a router to relay data packets, and therefore a wide range multi-hop network can be formed.
Ad hoc networks have come to find various applications for example in radio communication networks in disaster stricken areas or streaming between vehicles in ITS (Intelligent Transport Systems) (Masahiro Watanabe, “Wireless Ad Hoc Network,” Society of Automotive Engineers of Japan, Annual Spring Congresses in Yokohama, Humantronics Forum, pp. 18-23, May 2003).
Dynamic routing protocols that support multi-hop communication include table-driven protocols and on-demand protocols. The table-driven protocols allow control information related to routes to be regularly exchanged, so that a routing table is previously set, and known examples of the protocols include FSR (Fish-eye State Routing), OLSR (Optimized Link State Routing), and TBRPF (Topology Dissemination Based on Reverse-Path Forwarding).
The on-demand protocols allow a route to a destination to be made only when a demand for data transmission is issued, and known examples of the protocols include DSR (Dynamic Source Routing) and AODV (Ad Hoc On-Demand Distance Vector Routing).
In a conventional ad hoc network, when data communication is carried out from a source to a destination, the communication route is determined so that the number of hops between the source and the destination can be as small as possible (Guangyu Pei, et al., “Fisheye State Routing: A Routing Scheme for Ad Hoc Wireless Networks,” ICC2000. Commun., Volume 1, L.A., pp. 70-74, June 2000).
However, a radio wave environment is unstable and therefore a route with less hops does not necessarily constitute a good quality route. Therefore, it would be better to select only a stable route by some method, and one such known typical method is to introduce a signal strength threshold and another known method is to measure a packet loss rate.
The method by measuring the packet loss rate is effectively applied when there are a number of continuous packet losses.
As the method of determining the signal strength threshold, a method of extracting a stable route using the average of signal strengths has been known (Rohit Dube, Cynthia D. Rais, Kuang-Yeh Wang, and Satish K. Tripathi, “Signal Stability-Based Adaptive Routing (SSA) for Ad Hoc Mobile Networks,” IEEE Personal Communications, pp. 36-45, February 1997).